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CAN WE DETERMINE PENETRATION COEFFICIENTS AND DEPOSITION RATES FROM FIELD STUDIES? RESULTS OF A 37-PERSON PANEL STUDY IN NORTH CAROLINA
Wallace, L A. AND R W. Williams. CAN WE DETERMINE PENETRATION COEFFICIENTS AND DEPOSITION RATES FROM FIELD STUDIES? RESULTS OF A 37-PERSON PANEL STUDY IN NORTH CAROLINA. Presented at American Association for Aerosol Research, Atlanta, GA, Ocotober 4-8, 2004.
The primary study objectives are:
1.To quantify personal exposures and indoor air concentrations for PM/gases for potentially sensitive individuals (cross sectional, inter- and intrapersonal).
2.To describe (magnitude and variability) the relationships between personal exposure, and indoor, outdoor and ambient air concentrations for PM/gases for different sensitive cohorts. These cohorts represent subjects of opportunity and relationships established will not be used to extrapolate to the general population.
3.To examine the inter- and intrapersonal variability in the relationship between personal exposures, and indoor, outdoor, and ambient air concentrations for PM/gases for sensitive individuals.
4.To identify and model the factors that contribute to the inter- and intrapersonal variability in the relationships between personal exposures and indoor, outdoor, and ambient air concentrations for PM/gases.
5.To determine the contribution of ambient concentrations to indoor air/personal exposures for PM/gases.
6.To examine the effects of air shed (location, season), population demographics, and residential setting (apartment vs stand-alone homes) on the relationship between personal exposure and indoor, outdoor, and ambient air concentrations for PM/gases.
The contribution of outdoor particles to indoor concentrations is governed by three physical processes: air exchange, penetration, and deposition. Air exchange rates can be measured during field studies, but the other two parameters must be estimated. Over the past few years, half a dozen studies have attempted to estimate these parameters for PM2.5. In almost every case, the attempt has failed when applied to individual homes, although an average value across homes has sometimes been estimated, with uncertain reliability. This presentation attempts to estimate individual parameters for 36 homes, based on an EPA-sponsored study of personal exposures to PM2.5 for 37 persons with hypertension or cardiovascular disease in North Carolina. Personal, indoor and outdoor 24-h samples were collected for 7 days in each of four seasons in 2000-2001. PM results from the study have been previously reported (Williams et al., 2003a,b). All filters (>2000) were analyzed by X-ray fluorescence for sulfur among other elements. Because sulfur has few sources indoors, it can be used as a marker for PM of outdoor origin. Estimates of the penetration coefficient and deposition rate were made using both a linear and nonlinear approach involving the measured air exchange rate or its inverse. The approaches generally agreed among themselves, but both approaches resulted in predictions for five of the 36 homes that were physically impossible.
Although this work was reviewed by EPA and approved for publication, it may not necessarily reflect official Agency policy.
Record Details:Record Type: DOCUMENT (PRESENTATION/ABSTRACT)
Organization:U.S. ENVIRONMENTAL PROTECTION AGENCY
OFFICE OF RESEARCH AND DEVELOPMENT
NATIONAL EXPOSURE RESEARCH LABORATORY
HUMAN EXPOSURE AND ATMOSPHERIC SCIENCES DIVISION
EXPOSURE MEASUREMENTS & ANALYSIS BRANCH